Heat Pump Running Constantly Fix Heating Issues

Is It Normal for a Heat Pump to Run Constantly?

This is one of the most common concerns I hear from homeowners who've recently had a heat pump installed. The short answer is: heat pumps are designed to run for much longer periods than boilers but running constantly, all day and all night, without ever stopping, is not normal and usually points to a problem.

A gas boiler fires up intensely, heats the system quickly, and switches off. A heat pump works more like a fridge running steadily at a lower output for extended periods. In cold weather, it might run for 8–14 hours a day. In very cold weather, longer. But it should stop periodically, and it should be able to bring your home up to temperature and maintain it.

If your heat pump runs 24/7 and your home is still cold, or barely reaches temperature, that's a system struggling — not a system working efficiently.

Reason 1: The System Is Undersized for Your Home

The most fundamental cause of a heat pump that runs constantly and fails to heat the home is undersizing. Heat pump sizing should be based on a room-by-room heat loss calculation — the total amount of heat your home loses on the coldest day of the year (in most UK locations, the design temperature is around -2°C to -3°C).

If the heat pump was sized on floor area, a rule of thumb, or a previous boiler size, there's a real risk it's too small. Signs of undersizing: the system runs all day but the house still feels cold in cold weather, the backup electric heater activates frequently, and flow temperatures are pushed up high trying to compensate.

A well-insulated modern 3-bed semi might have a heat loss of 5–6kW. A typical older semi might be 8–10kW. A poorly insulated detached property could be 14kW+. If the installed heat pump doesn't match your actual heat loss, it will run constantly trying to compensate.

Reason 2: Radiators Are Too Small for Heat Pump Temperatures

Even if the heat pump itself is correctly sized, the system can still run constantly if the radiators aren't adequate. Heat pump radiators need to be significantly larger than boiler radiators because they work at a lower temperature difference from the room air.

The technical term is Delta T. At boiler temperatures (70–80°C flow), radiators work at Delta T 50 and produce their full rated output. At heat pump temperatures (40–45°C flow), radiators work at Delta T 20 and produce roughly 40% of their rated output. If radiators weren't upgraded when the heat pump went in, the system physically cannot deliver enough heat at efficient temperatures.

The common fix is to increase radiator size in the worst-performing rooms usually north-facing rooms, rooms with large windows, or rooms furthest from the heat pump.

Reason 3: Flow Temperature Set Too High, Masking the Real Problem

Sometimes a system runs constantly because the flow temperature has been set very high (55–60°C) to compensate for undersized radiators or poor insulation. The system runs constantly because it's fighting hard to maintain those high temperatures, and every degree above 45°C costs significantly more electricity.

This is a common commissioning patch set the flow temperature high so the homeowner doesn't complain that the house is cold, at the expense of efficiency and running costs. If your flow temperature is fixed above 50°C, it's worth investigating why.

Reason 4: Weather Compensation Not Configured

When weather compensation is working correctly, the heat pump reduces its flow temperature in mild weather and can run less hard, or stop more frequently. When it's disabled or set incorrectly, the system maintains full output regardless of outdoor temperature. On a mild October day at 12°C, this means the system is working far harder than necessary and cycling less efficiently.

It is also worth considering whether your system has a buffer tank and whether it is configured correctly — our guide on whether heat pumps need a buffer tank explains when they help and when they cause more problems than they solve.

Reason 5: Hydraulic Issues Heat Not Reaching All Areas

If the heating circuit isn't properly balanced, some radiators get too much flow and others too little. The rooms with restricted flow stay cold, the thermostat never triggers a satisfied signal, and the heat pump keeps running. Check whether some rooms are always warmer than others with TRVs fully open this is a sign of hydraulic imbalance.

How to Tell If Your System Is Genuinely Struggling

A few diagnostic questions to ask yourself: Does the heat pump run all day even when outdoor temperatures are above 8°C? Does your home reach the set thermostat temperature, or does it always fall slightly short? Does the backup electric heater activate regularly, not just during hard frosts? Are certain rooms consistently colder than others?

If you answered yes to two or more of these, the system almost certainly has a design or configuration issue that's causing it to run more than necessary.

If you are an installer supporting a customer whose system runs constantly and you want an independent technical perspective before recommending hardware changes, our Partner Installer Support is designed for exactly this situation. It provides structured third-party input on configuration, flow rates, and system behaviour — helping you identify whether the issue is a settings problem or something that genuinely requires further action.

What to Do Next

The starting point is to establish what your actual heat loss is and compare it to your installed heat pump output. We can review this remotely by looking at your property details, existing temperature and performance data, and system configuration. From there, we can identify whether the issue is sizing, radiator capacity, flow temperature, weather compensation, or hydraulic balance and give you specific, practical recommendations.